Engine sensors are used in many conventional engines to indirectly detect the presence of emissions such as oxides of nitrogen (NOx) and/or particulate matter (PM) in the exhaust stream. In diesel engines, for example, such sensors are sometimes used to measure manifold air temperature (MAT), manifold air pressure (MAP), and manifold air flow (MAF) of air injected into the engine intake manifold ahead of the engine combustion and aftertreatment devices. These sensed parameters are then analyzed in conjunction with other engine properties to adjust the performance characteristics of the engine.
In some designs, the vehicle may be equipped with an electronic control unit (ECU) capable of sending commands to actuators in order to control the engine, aftertreatment devices, as well as other powertrain components in order to achieve a desired balance between engine power and emissions. To obtain an estimate of the emissions outputted by the engine, an engine map modeling the engine combustion may be constructed during calibration to infer the amount of NOx and PM produced and emitted from the engine. Depending on the particular time during the drive cycle, the ECU may adjust various actuators to control the engine in a desired manner to compensate for both engine performance and emissions constants. Typically, there is a trade off between engine performance and the amount of acceptable NOx and/or PM that can be emitted from the engine. At certain times during the drive cycle such as during cruising speeds, for example, it may be possible to control the engine in order to reduce the amount of NOx and/or PM emitted without significantly sacrificing engine performance. Conversely, at other times during the drive cycle such as during hard acceleration, it may be necessary to sacrifice emissions performance in order to increase engine power. At other times, an aftertreatment device may be actively regenerated, and requires different conditions achievable in part by changing the signals to the actuators.
The efficacy of the engine model and/or aftertreatment device is often dependent on the accuracy in which the model assumptions match the actual vehicle operating conditions. Conditions such as engine wear, fuel composition, and ambient air composition, for example, may change quickly as a result of changing ambient conditions or slowly over the life of the vehicle, in either case affecting the ability of the engine model to accurately predict actual vehicle operating conditions. Other factors such as changes in fuel type may also have an impact on the model assumptions used to estimate actual operating conditions. As a result, the engine model can become outdated and ineffective.